A transactional model of the influence of a congenital risk variable for first- and second born children on families varying in healthy functioning and of the influence of families on children will be tested. Through testing the model, the relative importance of congenital, sibling, parent-child, marital, parental, and whole family characteristics for behavior problems in children and family coping will be assessed. Through the model, we will assess when socialization is family-driven (family coping remains high, independent of one or two children who vary in risk for congenitally related difficulties) from socialization that is child- driven (families with congenitally one or two easy children cope well while those with congenitally difficult children cope less well.) The need for research on behavior problems in children that encompasses more than one causal mechanism has been recognized increasingly and emphasized in recent reviews. By identifying the relative importance of congenital, sibling, parent- child relationship, marital, parental and whole family characteristics to behavior problems in both first- and second born children, appropriate foci for intervention (either as prevention or treatment) can be identified. There is also a need for information on families with pre-school children from nonclinical populations. The majority of child behavior problems are not brought to the attention of professionals until the child is enrolled in school. Much of the research on the effects of the whole family has come from clinical studies of school-age children or adolescents. No research on marital and family effects on child behavior has focused specifically on young children and none has focused on how congenital risk factors in siblings affect families. The importance of early intervention suggests the need to study this age group. While clinical studies are important, it is also vital to obtain information on a wide range of families in order to put clinical studies in an appropriate context. Research participants are 160 families recruited through radio announcements and newspaper advertisements. Families with firstborns have been observed, have filled out questionnaires on family coping health, and childbearing. The second borns will now be followed for 2 years along with continued assessment of firstborns. Multivariate analyses will examine the joint interaction of sibling congenital characteristics and family measures in predicting behavior problems of both children over four years.